1. Field of the Invention
The present invention is directed to electronic circuitry protection devices. More particular, the present invention pertains to a fuse for interfacing a power source with components on a printed wiring board while protecting the components from electrostatic discharges.
2. Description of the Related Art
Protection devices such as fuses are well known and are used to safeguard electrical equipment from current surges delivered by a power source. Such fuses are typically connected between a power source and the electrical equipment and become open circuits when a current surge predeterminantly exceeding the maximum current rating of the fuse is received. Fuses may also be exposed to voltage surges such as electrostatic discharges or arcs that are often generated when electrical equipment is touched by, for example, a person.
As is known in the art, when voltage spikes, in general, and electrostatic discharges in particular are generated, the spikes will travel along a path of least resistance. Fuses are designed with this principle in mind to allow a generated spike to be discharged without damaging the electrical equipment interfaced with the fuse, i.e. to provide a low resistance path to common ground. Because electrostatic shocks are fairly common, such as those caused by human interaction with electronic equipment, such equipment as well as the fuses connected thereto must be tested to determine whether they can withstand such voltage spikes.
For example, in the telecommunications industry miniature fuses are commonly used to interface power supplies with electrical components mounted to a printed wiring board. Specifically, each fuse seats within a fuse holder connected to the printed wiring board and consists of a fuse body, typically of plastic material, to which a fuse element and a fuse indicator are connected. A transparent indicator window is positioned over the fuse indicator and is friction-fitted to the fuse body.
Prior to commercial use, telecommunications equipment as well as the fuses through which power is supplied thereto are administered an electrostatic discharge test to determine whether the equipment meets predetermined standards in the industry or otherwise dictated by manufacturer or user demands. Such tests are administered by applying electrostatic shocks of approximately 15 KV to various regions of the devices under test. For example, as a part of such testing, electrostatic shocks are applied to various regions of the fuses such as the fuse holder and fuse window to determine whether the shocks are safely discharged or dissipated, e.g. to ground, without damaging the electrical components connected to the fuse. When the test is administered to the fuse holder, the shock is typically discharged without damaging the electrical components. However, when the test is administered to the fuse window or to the fuse body of currently utilized fuses at a location proximate the fuse window, an air gap inherently present between the window and body serves as a conduit which detrimentally directs the shock to the fuse element and, consequently, to the electronic equipment. The result, of course, is equipment damage.
Prior art techniques employed to alleviate this problem involve placing a small metal door or panel in close proximity to the window to provide a discharge path for the arc. Such a technique, however, is costly, burdensome and obstructs the view of the fuse indicator, thus making difficult visual inspection of the condition of the fuse.